Bacteria help to clean up Deepwater Horizon spill

Zoom in on the Deepwater Horizon oil slick and you will find a motley community of critters hard at work breaking down the oil: bacteria.

At the annual meeting of the American Society for Microbiology in San Diego, California, this week, Jay Grimes of the University of Southern Mississippi in Hattiesburg reported that over the past few years, researchers have found that dozens of different kinds of marine bacteria have a healthy appetite for oil.

He said that water samples from the Gulf of Mexico are showing signs that marine bacteria are already pitching in to help with clean-up efforts, and that populations of these bacteria in this area are likely to boom as they feast on the oil from the Deepwater Horizon disaster.

Among these are members of the Vibrio family, which includes the species that causes cholera. Grimes cautions that there is no evidence that this species is one of those that breaks down oil, although other Vibrios that cause human infections do.

"The Vibrios use breakdown products of oil," says Rita Colwell of the University of Maryland in College Park. "When [the oil from Deepwater Horizon] reaches the estuary, Vibrios very likely will increase."

Feasting bacteria

Colwell says that the greatest risk of bacterial infection in the Gulf comes from Vibrio fish pathogens and other species that commonly infect shellfish. Some of these can cause disease in humans.

Grimes's research department had the only research vessel, the R/V Pelican, on the scene until BP sent one in this week. It brought back samples of oil droplets that already had Vibrios clustered around them. Low oxygen levels were also detected near patches of oil, a sign that bacteria are feasting.

Crucially, R/V Pelican happened to be in the area when Deepwater Horizon blew up. That means the team could immediately collect water samples to test for bacterial populations from areas that were threatened by the spill but had not yet been contaminated. The work is on-going and will be vital in future studies of how the spill has changed local ecosystems.

"Now we plan to see how the microbial community evolves when you give it oil," says Grimes. He hopes to screen bacteria from oil-affected water for the DNA of oil-eating enzymes, and use this to determine their species.

"This blowout could permanently reshuffle the microbial community in the Gulf," Grimes says. In previous research he found that Vibrio became the dominant type of marine bacteria off the south-eastern US as oil tanker traffic increased after the 1970s.

Long-term threat

For now the oil mainly threatens larval fish clinging to the underside of mats of seaweed. "I hope most of the oil will stay out to sea," says Grimes. "It may kill a year's production of fish, but if it hits the coastal marshes, it could be there for a decade." At particular risk are coastal salt marshes.

Ultimately, the tiny bacteria which Grimes and his colleagues are poring over will finish the Deepwater clean-up operation. Speaking at the San Diego meeting, Ron Atlas of the University of Louisville, Kentucky, said that the oil-eating microbes already present in seawater will be enough to get rid of any oil that is not physically removed by the clean-up crews – except for insoluble, tarry material that poses little toxic risk.

Atlas, who managed the "bioremediation" of the 1989 Exxon Valdez spill in Alaska, says the bacterial process will be helped if fertiliser is added to the water, as then the oil-eaters will have the nitrogen and phosphate they need to grow.

Fertiliser has already been used to aid the bacterial breakdown of oil that has hit the shore, but it could also help bacteria in the open sea if it is added to the detergents that are being used to disperse the oil. The fertiliser lodges in the surface of the oil droplets created by the detergents, he says – right where the bacteria can use them.

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